This invention relates to a method of manufacturing a double-structure sound absorbing wall for effectively preventing noise to be propagated to the interior or exterior of a motor vehicle, such as motor car or motor truck. The noise is produced due to vibrations of an engine and auxiliary devices therefor which are mounted in the engine room of the vehicle.
In a conventional construction of the sound absorbing wall, for example a dash panel dividing the compartment and the engine room, a known suitable sound insulating material is simply adhered or fixed to the panel to prevent the propagation of noise. However, such a construction is insufficient to prevent the propagation of noise. In the other construction, a dash panel is a double-structure having a cavity defined by inner and outer plates. Such a dash panel is provided with an opening for inserting a steering shaft and holes for inserting and attaching many kinds of equipments such as a brake master cylinder, and sealing member having a waterproof function is fitted over a joined peripheral portion of the inner and outer plates. However, since the cavity is only formed as a hollow portion, it is difficult to prevent the propagation of noise and vibration of the engine. Also, fitting of the sealing member takes much time, and rust will be appeared on the inner and outer plates by entering of water into the cavity.